The present invention relates to systems for repairing metal components, such as gas turbine engine components. In particular, the present invention relates to microwave brazing systems for repairing metal components.
Superalloys of nickel, cobalt, and iron, single crystal or equiaxed, are typically employed in gas turbine engine components due to the high mechanical strengths and creep resistances obtained with such alloys. Because gas turbine engine components are exposed to extreme temperatures and pressures, high mechanical strengths and creep resistances are required to preserve the integrity of the engine over the course of operation. However, over time, exposed portions of the components are subject to wear, cracking, and other degradations, which can lead to decreases in operational efficiencies.
Due to economic factors, it is common practice in the aerospace industry to restore turbine engine components rather than replace them. Such restorations desirably restore damaged regions of the engine components to their original dimensions. Engine cracks are typically repaired with brazing operations, which subject the single crystal alloys of the engine components to high temperatures (e.g., 1200° C./2200° F.) for extended durations (e.g., 10 hours). Exposure to the high temperatures for the extended durations, however, reduces the low-temperature (e.g., 815° C.-870° C./1500° F.-1600° F.) creep resistances of the single crystal alloys. This is believed to be due to coarsening of the gamma prime (γ′) phases of the single crystal alloys, which is measurable by increases in the average particle sizes of the γ′ phases. The reduction of the low-temperature creep resistances can cause the alloy structures of the engine components to creep under the applied temperatures and pressures during operation, thereby also reducing operational efficiencies.
One technique for restoring engine components that substantially preserves the low-temperature creep resistances of single crystal alloys involves microwave brazing. Microwave brazing uses microwave-wavelength radiation to melt and fuse a brazing alloy with the base material of the damaged engine component. The microwave brazing process reduces the duration and temperature that the base material is exposed to, thereby substantially preserving the low-temperature creep resistances of the single crystal alloys. A microwave brazing process is typically performed in a brazing chamber under vacuum to provide a uniform braze and to reduce the risk of generating glow discharges and plasmas. However, pressure gauges used to measure the reduced pressure within the brazing chamber are sensitive to the microwaves used in the microwave brazing process. This may provide erroneous pressure measurements during the microwave brazing process, thereby reducing the ability to obtain the desired vacuum environment. As such, there is a need for a system capable of providing accurate pressure measurements during microwave brazing processes.